The one thing I don't get about the en echelon attack is that it's supposed to generally follow the Emmitsburg Road. But Hancock and Sickles (if he's where he should be) would be several hundred yards away on Cemetery Ridge able to strike the Confederates moving across the Union front. Or is the attack suppose to sweep away the Feds where they are deployed (my guess)? Am I missing something here? Is Lee hoping to draw the Feds off the ridge for the climactic battle? Somebody paint me a picture.

You have it pretty clearly, other than drawing US forces off of the ridge.

The CS attack plan was drawn up in the morning. By late afternoon, the Federal line was not where Lee wanted it to be...